SPOILERS: Stop reading if you don't want to know what happens.
And seriously, do we really need a female Fight Club? The whole split personality thing that Hollywood is so fascinated with has gotten stale. For the next several years, if you make a movie or write a story and the only way it makes sense is that the protagonist is also the antagonist because of a split personality, then you probably should just stop writing because your story is probably crap. There are only a handful of people in the whole world that have split personalities but if you believe and are influenced by Hollywood you'll be thinking there are thousands and thousands of people like that.